netfilter: nf_queue: Make the queue_handler pernet

Florian Weber reported:
> Under full load (unshare() in loop -> OOM conditions) we can
> get kernel panic:
>
> BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
> IP: [<ffffffff81476c85>] nfqnl_nf_hook_drop+0x35/0x70
> [..]
> task: ffff88012dfa3840 ti: ffff88012dffc000 task.ti: ffff88012dffc000
> RIP: 0010:[<ffffffff81476c85>]  [<ffffffff81476c85>] nfqnl_nf_hook_drop+0x35/0x70
> RSP: 0000:ffff88012dfffd80  EFLAGS: 00010206
> RAX: 0000000000000008 RBX: ffffffff81add0c0 RCX: ffff88013fd80000
> [..]
> Call Trace:
>  [<ffffffff81474d98>] nf_queue_nf_hook_drop+0x18/0x20
>  [<ffffffff814738eb>] nf_unregister_net_hook+0xdb/0x150
>  [<ffffffff8147398f>] netfilter_net_exit+0x2f/0x60
>  [<ffffffff8141b088>] ops_exit_list.isra.4+0x38/0x60
>  [<ffffffff8141b652>] setup_net+0xc2/0x120
>  [<ffffffff8141bd09>] copy_net_ns+0x79/0x120
>  [<ffffffff8106965b>] create_new_namespaces+0x11b/0x1e0
>  [<ffffffff810698a7>] unshare_nsproxy_namespaces+0x57/0xa0
>  [<ffffffff8104baa2>] SyS_unshare+0x1b2/0x340
>  [<ffffffff81608276>] entry_SYSCALL_64_fastpath+0x1e/0xa8
> Code: 65 00 48 89 e5 41 56 41 55 41 54 53 83 e8 01 48 8b 97 70 12 00 00 48 98 49 89 f4 4c 8b 74 c2 18 4d 8d 6e 08 49 81 c6 88 00 00 00 <49> 8b 5d 00 48 85 db 74 1a 48 89 df 4c 89 e2 48 c7 c6 90 68 47
>

The simple fix for this requires a new pernet variable for struct
nf_queue that indicates when it is safe to use the dynamically
allocated nf_queue state.

As we need a variable anyway make nf_register_queue_handler and
nf_unregister_queue_handler pernet.  This allows the existing logic of
when it is safe to use the state from the nfnetlink_queue module to be
reused with no changes except for making it per net.

The syncrhonize_rcu from nf_unregister_queue_handler is moved to a new
function nfnl_queue_net_exit_batch so that the worst case of having a
syncrhonize_rcu in the pernet exit path is not experienced in batch
mode.

Reported-by: Florian Westphal <fw@strlen.de>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/net/netfilter/nf_queue.h

@@ -28,8 +28,8 @@ struct nf_queue_handler {
 						struct nf_hook_ops *ops);
 };
 
-void nf_register_queue_handler(const struct nf_queue_handler *qh);
-void nf_unregister_queue_handler(void);
+void nf_register_queue_handler(struct net *net, const struct nf_queue_handler *qh);
+void nf_unregister_queue_handler(struct net *net);
 void nf_reinject(struct nf_queue_entry *entry, unsigned int verdict);
 
 void nf_queue_entry_get_refs(struct nf_queue_entry *entry);

include/net/netns/netfilter.h

@@ -5,11 +5,13 @@
 
 struct proc_dir_entry;
 struct nf_logger;
+struct nf_queue_handler;
 
 struct netns_nf {
 #if defined CONFIG_PROC_FS
 	struct proc_dir_entry *proc_netfilter;
 #endif
+	const struct nf_queue_handler __rcu *queue_handler;
 	const struct nf_logger __rcu *nf_loggers[NFPROTO_NUMPROTO];
 #ifdef CONFIG_SYSCTL
 	struct ctl_table_header *nf_log_dir_header;

net/netfilter/nf_queue.c

@@ -26,23 +26,21 @@
  * Once the queue is registered it must reinject all packets it
  * receives, no matter what.
  */
-static const struct nf_queue_handler __rcu *queue_handler __read_mostly;
 
 /* return EBUSY when somebody else is registered, return EEXIST if the
  * same handler is registered, return 0 in case of success. */
-void nf_register_queue_handler(const struct nf_queue_handler *qh)
+void nf_register_queue_handler(struct net *net, const struct nf_queue_handler *qh)
 {
 	/* should never happen, we only have one queueing backend in kernel */
-	WARN_ON(rcu_access_pointer(queue_handler));
-	rcu_assign_pointer(queue_handler, qh);
+	WARN_ON(rcu_access_pointer(net->nf.queue_handler));
+	rcu_assign_pointer(net->nf.queue_handler, qh);
 }
 EXPORT_SYMBOL(nf_register_queue_handler);
 
 /* The caller must flush their queue before this */
-void nf_unregister_queue_handler(void)
+void nf_unregister_queue_handler(struct net *net)
 {
-	RCU_INIT_POINTER(queue_handler, NULL);
-	synchronize_rcu();
+	RCU_INIT_POINTER(net->nf.queue_handler, NULL);
 }
 EXPORT_SYMBOL(nf_unregister_queue_handler);
 
@@ -103,7 +101,7 @@ void nf_queue_nf_hook_drop(struct net *net, struct nf_hook_ops *ops)
 	const struct nf_queue_handler *qh;
 
 	rcu_read_lock();
-	qh = rcu_dereference(queue_handler);
+	qh = rcu_dereference(net->nf.queue_handler);
 	if (qh)
 		qh->nf_hook_drop(net, ops);
 	rcu_read_unlock();
@@ -122,9 +120,10 @@ int nf_queue(struct sk_buff *skb,
 	struct nf_queue_entry *entry = NULL;
 	const struct nf_afinfo *afinfo;
 	const struct nf_queue_handler *qh;
+	struct net *net = state->net;
 
 	/* QUEUE == DROP if no one is waiting, to be safe. */
-	qh = rcu_dereference(queue_handler);
+	qh = rcu_dereference(net->nf.queue_handler);
 	if (!qh) {
 		status = -ESRCH;
 		goto err;

net/netfilter/nfnetlink_queue.c

@@ -1377,21 +1377,29 @@ static int __net_init nfnl_queue_net_init(struct net *net)
 			 net->nf.proc_netfilter, &nfqnl_file_ops))
 		return -ENOMEM;
 #endif
+	nf_register_queue_handler(net, &nfqh);
 	return 0;
 }
 
 static void __net_exit nfnl_queue_net_exit(struct net *net)
 {
+	nf_unregister_queue_handler(net);
 #ifdef CONFIG_PROC_FS
 	remove_proc_entry("nfnetlink_queue", net->nf.proc_netfilter);
 #endif
 }
 
+static void nfnl_queue_net_exit_batch(struct list_head *net_exit_list)
+{
+	synchronize_rcu();
+}
+
 static struct pernet_operations nfnl_queue_net_ops = {
-	.init	= nfnl_queue_net_init,
-	.exit	= nfnl_queue_net_exit,
-	.id	= &nfnl_queue_net_id,
-	.size	= sizeof(struct nfnl_queue_net),
+	.init		= nfnl_queue_net_init,
+	.exit		= nfnl_queue_net_exit,
+	.exit_batch	= nfnl_queue_net_exit_batch,
+	.id		= &nfnl_queue_net_id,
+	.size		= sizeof(struct nfnl_queue_net),
 };
 
 static int __init nfnetlink_queue_init(void)
@@ -1412,7 +1420,6 @@ static int __init nfnetlink_queue_init(void)
 	}
 
 	register_netdevice_notifier(&nfqnl_dev_notifier);
-	nf_register_queue_handler(&nfqh);
 	return status;
 
 cleanup_netlink_notifier:
@@ -1424,7 +1431,6 @@ out:
 
 static void __exit nfnetlink_queue_fini(void)
 {
-	nf_unregister_queue_handler();
 	unregister_netdevice_notifier(&nfqnl_dev_notifier);
 	nfnetlink_subsys_unregister(&nfqnl_subsys);
 	netlink_unregister_notifier(&nfqnl_rtnl_notifier);